I have the first genration Pi in my Stratux, and it sits on the glareshield of the Cessna 340 right on top of the audio panel, a PSE 8000. I have over 250 hours on the Stratux with no RFI problems on any radio. It could be that the planes having problems have ground loops built into the plane because of bad grounding of the mic and audio jacks. All jacks should have a separate ground wire from each ground pin on a jack that goes back to the ground stud on the back of the audio panel. Grounding to the airframe for convenience is a no-no.
Dick Welsh